Reflection and refraction optical system and projection exposure apparatus using the same

ABSTRACT

A reflection and refraction optical system includes a polarization beam splitter, a concave mirror, a lens group and a quarter waveplate, wherein an additional waveplate is provided to transform S-polarized light from the polarization beam splitter into circularly polarized light.

This application is a division of application Ser. No. 08/164,539 filedDec. 10, 1993.

FIELD OF THE INVENTION AND RELATED ART

This invention relates generally to an imaging optical system such as areflection and refraction optical system and, more particularly, to areflection and refraction optical system usable for imaging a finepattern in the manufacture of microdevices such as semiconductor devices(such as ICs or LSIs), image pickup devices (such as CCDs) or displaydevices (such as liquid crystal panels). According to another aspect,the invention is concerned with a projection exposure apparatus usingsuch a reflection and refraction optical system.

The degree of integration of a semiconductor device such as IC or LSI isincreasing, and fine processing technology for a semiconductor wafer isbeing improved considerably. In the projection exposure technique whichis the main portion of fine processing technology, the resolution hasbeen increased to a level allowing formation of an image of a linewidthnot greater than 0.5 micron.

The resolution can be improved by shortening the wavelength of lightused for the exposure process. However, the shortening of the wavelengthrestricts the glass materials usable for a projection lens system, andcorrection of chromatic aberration becomes difficult to attain.

A projection optical system with which the difficulty of correctingchromatic aberration can be reduced, may be a reflection and refractionoptical system comprising a concave mirror and a lens group, wherein theimaging function is mainly attributed to the power of the concavemirror.

Such reflection and refraction optical system may include a polarizationbeam splitter, a quarter waveplate and a concave mirror, disposed inthis order from the object plane side. Light from the object plane maypass through the polarization beam splitter and the quarter waveplate,it may be reflected by the concave mirror. After this, the light maypass through the quarter waveplate and the polarization beam splitter,and it may be imaged upon an image plane. The combination of apolarization beam splitter and a quarter waveplate may be effective toreduce the loss of light. However, the use of rectilinearly polarizedlight for the imaging process may involve a problem in the formation ofa fine image of a linewidth not greater than 0.5 micron because theimaging performance may change in dependence upon the orientation(lengthwise direction) of a (linear) pattern on the object plane.

As an example, the contrast of an image of 0.2 micron, which can beformed by using a projection optical system of a numerical aperture(N.A.) of 0.5 and a design wavelength 248 nm together with a phase shiftmask (line-and-space pattern), is changeable by about 20%, depending onwhether the direction of polarization of light used for the imagingprocess is parallel to or perpendicular to the lengthwise direction ofthe pattern.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an improved imagingoptical system effective to solve the problem described above.

It is another object of the present invention to provide an improvedreflection and refraction optical system effective to solve the problemdescribed above.

It is a further object of the present invention to provide an improvedprojection exposure apparatus which is free from the problem describedabove.

An imaging optical system according to the present invention may includea polarization beam splitter, a quarter waveplate and a reflectionmirror which may be disposed in this order from an object plane. Lightfrom the object plane may pass through the polarization beam splitterand the quarter waveplate, and it may be reflected by the reflectionmirror. The reflected light may pass through the quarter waveplate andthe polarization beam splitter, and then it may be imaged upon an imageplane. Means may be provided between the polarization beam splitter andthe image plane, for changing the plane of polarization of polarizedlight from the polarization beam splitter.

A reflection and refraction optical system according to the presentinvention may include a polarization beam splitter, a quarter waveplateand a concave reflection mirror which may be disposed in this order froman object plane. Light from the object plane may pass through thepolarization beam splitter and the quarter waveplate, and it may bereflected by the concave reflection mirror. The reflected light passthrough again the quarter waveplate and the polarization beam splitter,and then it may be imaged upon an image plane. Means may be providedbetween the polarization beam splitter and the image plane, for changingthe plane of polarization of polarized light from the polarization beamsplitter.

A projection exposure apparatus according to the present invention mayinclude projection optical system for projecting a pattern of a maskonto a substrate to be exposed. The projection optical system maycomprises a polarization beam splitter, a quarter waveplate and aconcave reflection mirror which may be disposed in this order from themask. Light from the mask may pass through the polarization beamsplitter and the quarter waveplate, and it may be reflected by theconcave reflection mirror. The reflected light may again pass throughthe quarter waveplate and the polarization beam splitter, and then itmay be directed to the substrate such that the pattern of the mask maybe imaged upon the substrate. Means may be provided between thepolarization beam splitter and the image plane, for changing the planeof polarization of polarized light from the polarization beam splitter.

A reflection and refraction optical system or a projection exposureapparatus according to the present invention may suitably used for themanufacture of microdevices such as semiconductor devices (such as ICsor LSIs), image pickup devices (such as CCDs) or display devices (suchas liquid crystal panels). Particularly, a reflection optical system ofthe present invention when arranged to provide a reduction magnificationand used as a projection optical system in combination with deepultraviolet light, may be effective to image a fine device pattern of alinewidth not greater than 0.5 micron.

These and other objects, features and advantages of the presentinvention will become more apparent upon a consideration of thefollowing description of the preferred embodiments of the presentinvention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a reduction projection exposure apparatusfor the manufacture of semiconductor devices, according to an embodimentof the present invention.

FIG. 2 is a flow chart of semiconductor device manufacturing processes.

FIG. 3 is a flow chart, illustrating details of a wafer process.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates a reduction projection exposure apparatus accordingto an embodiment of the present invention, for the manufacture ofsemiconductor devices.

Denoted in FIG. 1 at 1 is a reticle having a circuit pattern to betransferred to a wafer 9 for the manufacture of semiconductor devices.The reticle 1 is held on an object plane of a reflection and refractionoptical system 100, by means of a reticle stage (not shown). The circuitpattern of the reticle 1 can be illuminated with deep ultraviolet lightof a wavelength λ(<300 (nm)) from an illumination system (not shown),with uniform illuminance. Divergent light from the illuminated reticle1, including zeroth order and first order diffraction light, is receivedby a first lens group 2 having a positive refracting power. The firstlens group 2 serves to transform the received divergent light into aparallel light consisting of a flux of light rays parallel to theoptical axis AX, and it projects the light on a polarization beamsplitter 3. The parallel light incident on the polarization beamsplitter 3 passes through the same, and then it passes through a quarterwaveplate 4 and enters a second lens group 5 having a negativerefracting power.

The parallel light passing through the polarization beam splitter 3 andimpinging on the lens group 5 is P-polarized light with respect to thedividing plane 3a of the polarization beam splitter 3. Of the parallellight impinging on the polarization beam splitter 3, the light which isS-polarized light with respect to the dividing plane 3a is reflected bythat plane 3a upwardly as viewed in the drawing.

Further, the quarter waveplate 4 is arranged and disposed so as totransform P-polarized light, entering it from the left hand side in thedrawing, into circularly polarized light and also to transformcircularly polarized light, entering it from the right hand side in thedrawing, into S-polarized light.

The second lens group serves to transform the parallel light, passingthrough the polarization beam splitter 3 and the quarter waveplate 4,into divergent light and to project the same on a concave mirror 6. Theconcave mirror 6 has a spherical reflection surface which isrotationally symmetrical with respect to the optical axis AX. Theconcave mirror 6 serves to reflect and converge the received divergentlight back to the lens group 5. The light passes through the second lensgroup 5 and the quarter waveplate 4, and it is projected to thepolarization beam splitter 3. Due to the function of the quarterwaveplate 4, the light reflected and converged by the concave mirror 6and impinging again on the polarization beam splitter 3 is S-polarizedlight with respect to the dividing plane 3a. As a consequence, thisre-entering light is reflected by the dividing plane 3a of thepolarization beam splitter 3 downwardly as viewed in the drawing.

Disposed below the polarization beam splitter 3 are a polarization planechanging means 7 and a third lens group 8 having a positive refractingpower. Further below the third lens group 3, there is a silicon wafer 9used in the manufacture of semiconductor devices, which wafer is held bya movable X-Y stage (not shown) so that its surface, to be exposed,coincides with the image plane of the reflection and refraction opticalsystem 100.

The polarization plane changing means 7 comprises a quarter waveplatewhich serves to transform the light, reflected by the dividing plane 3aof the polarization beam splitter 3, into circularly polarized lightwhich in turn is projected on the third lens group 8. The third lensgroup 8 serves to collect the circularly polarized light from thequarter waveplate of the polarization plane changing means 7, and areduced image of the circuit pattern of the reticle I is formed on thewafer 9.

The projection exposure apparatus of this embodiment uses a polarizationbeam splitter (3), but it is arranged to form an image from circularlypolarized light. As a consequence, for imaging fine patterns, there doesnot occur non-uniformness of resolution between different patterns whichmight otherwise result from the polarization dependency of the pattern.In other words, the projection exposure apparatus of this embodimentassures constant resolution independently of the type (orientation) ofthe fine pattern of a reticle 1 used.

In the projection exposure apparatus of this embodiment, the reticlestage for supporting the reticle I may be disposed horizontally and areflection mirror may be provided between the reticle stage and the lensgroup 2 so as to deflect the optical axis AX by 45 deg. In that case,the overall size of the apparatus can be made small.

The projection exposure apparatus of this embodiment may be arranged toexecute step-and-repeat exposures according to which the X-Y stage onwhich the wafer 9 is placed is moved stepwise to form circuit patternson substantially the whole surface of the wafer 9. Alternatively, it maybe arranged to execute step-and-scan exposures wherein the X-Y stage onwhich the wafer 9 is placed is moved stepwise and so as to permitscanning.

The projection exposure apparatus of this embodiment may be used incombination with a phase shift mask as the reticle 1. In that case, itmay be possible to image a pattern of a smaller linewidth. Further, thestructure of the illumination system (not shown) may be modified into anoblique illumination system by which the reticle 1 is illuminated alonga direction inclined with respect to the optical axis AX. Also in thatcase, a pattern of smaller linewidth may be imaged.

The projection exposure apparatus of this embodiment may use a lightsource comprising a KrF excimer laser (λ≃248 nm), an ArF excimer laser(λ≃193 nm) or an ultra high pressure Hg lamp (emission line spectrum:λ≃250 nm), for example.

In another embodiment according to the present invention, a projectionexposure apparatus such as described above may include a polarizationplane changing means 7 comprising a half waveplate being made rotatableabout the optical axis AX. When such polarization plane changing meansis used, it is possible to change the plane of polarization of lightfrom the polarization beam splitter 3 in accordance with the orientationof a fine pattern of a reticle 1 used. Thus, imaging with polarizationlight of increased resolution (non-deteriorated resolution) may alwaysbe assured.

For example, in the case where a fine pattern of a reticle 1 has alengthwise direction laid longitudinally (up and down) as viewed in thedrawing, the rotational angle of the half waveplate 7 may be so set asto transform the plane of polarization of the light from thepolarization beam splitter 3, from S-polarized light into P-polarizedlight.

In the case where a fine pattern of a reticle 1 has a lengthwisedirection laid perpendicularly to the sheet of the drawing, therotational angle of the half waveplate 7 may be set so as to retain theplane of polarization (S-polarization) of the light from thepolarization beam splitter 3.

In the case where a fine pattern of a reticle 1 has an orientation,extending both longitudinally as viewed in the drawing and perpendicularto the sheet of the drawing, (i.e., a cross pattern), the rotationalangle of the half waveplate 7 may be so set as to transform the plane ofpolarization (S-polarization) of the light from the polarization beamsplitter 3, into polarized light of 45 deg. with respect to both of theS-polarization and P-polarization.

In a further embodiment according to the present invention, thewaveplate of the polarization plane changing means 7 may comprise anelectro-optic crystal device (EO optical-modulator) whose birefringence(double refraction) characteristic can be controlled electrically.

Next, an embodiment of a method of manufacturing semiconductor devicesbased on the reticle 1 and the projection exposure apparatus of FIG. 1,will be explained.

FIG. 2 is a flow chart of the sequence of manufacturing a semiconductordevice such as a semiconductor chip (e.g. IC or LSI), a liquid crystalpanel, or a CCD, for example. Step 1 is a design process for designingthe circuit of a semiconductor device. Step 2 is a process formanufacturing a mask on the basis of the circuit pattern design. Step 3is a process for manufacturing a wafer by using a material such assilicon.

Step 4 is a wafer process which is called a pre-process wherein, byusing the so prepared mask and wafer, circuits are practically formed onthe wafer through lithography. Step 5 subsequent to this is anassembling step which is called a post-process wherein the waferprocessed by step 4 is formed into semiconductor chips. This stepincludes assembling (dicing and bonding) and packaging (chip sealing).Step 6.is an inspection step wherein an operability check, a durabilitycheck, and so on, of the semiconductor devices produced by step 5 arecarried out. With these processes, semiconductor devices are finishedand they are shipped (step 7).

FIG. 3 is a flow chart showing details of the wafer process. Step 11 isan oxidation process for oxidizing the surface of a wafer. Step 12 is aCVD process for forming an insulating film on the wafer surface. Step 13is an electrode forming process for forming electrodes on the wafer byvapor deposition. Step 14 is an ion implanting process for implantingions to the wafer. Step 15 is a resist process for applying a resist(photosensitive material) to the wafer. Step 16 is an exposure processfor printing, by exposure, the circuit pattern of the mask on the waferthrough the exposure apparatus described above. Step 17 is a developingprocess for developing the exposed wafer. Step 18 is an etching processfor removing portions other than the developed resist image. Step 19 isa resist separation process for separating the resist material remainingon the wafer after being subjected to the etching process. By repeatingthese processes, circuit patterns are superposedly formed on the wafer.

As described hereinbefore, the present invention according to an aspectthereof provides an imaging optical system or a reflection andrefraction optical system, by which high resolution is assuredindependently of the type (orientation) of a fine pattern of an objectto be projected. Thus, the present invention according to another aspecteffectively assures an improved projection exposure apparatus havingsuperior projection exposure performance and based on a reflection andrefraction optical system, or a method of manufacturing various devicesthrough the use of a reflection and refraction optical system.

While the invention has been described with reference to the structuresdisclosed herein, it is not confined to the details set forth and thisapplication is intended to cover such modifications or changes as maycome within the purposes of the improvements or the scope of thefollowing claims.

What is claimed is:
 1. An imaging optical system, comprising:a polarization beam splitter; a quarter waveplate; a reflection mirror; and polarization plane changing means; wherein a beam from an object plane is projected by way of said polarization beam splitter and said quarter waveplate upon said reflection mirror, wherein the projected beam is reflected by said reflection mirror and is projected by way of said quarter waveplate and said polarization beam splitter upon an image plane, and wherein said polarization plane changing means is disposed between said polarization beam splitter and the image plane to change the plane of polarization of the beam from said beam splitter, wherein said polarization plane changing means comprises a half waveplate effective to transform a beam from said polarization beam splitter into a rectilinearly polarized beam, being polarized in a desired direction.
 2. An imaging optical system, comprising:a polarization beam splitter; a quarter waveplate; a concave mirror; and a half waveplate: wherein a beam from an object plane is projected by way of said polarization beam splitter and said quarter waveplate upon said concave mirror, wherein the projected beam is reflected by said concave mirror and is projected by way of said quarter waveplate and said polarization beam splitter upon an image plane, and wherein said half waveplate is disposed between said polarization beam splitter and the image plane to change the beam from said beam splitter to a linearly polarized beam, being polarized in a desired direction.
 3. An imaging optical system according to claim 2, further comprising a first lens group disposed between the object plane and said polarization beam splitter and a third lens group disposed between said polarization beam splitter and the image plane.
 4. An imaging optical system according to claim 3, wherein said first lens group is effective to transform a beam from the object plane into a parallel beam and to project the parallel beam to said polarization beam splitter.
 5. An imaging optical system according to claim 4, further comprising a second lens group disposed between said polarization beam splitter and said concave mirror, wherein said second lens group is effective to transform the parallel beam from said polarization beam splitter into a divergent beam and to direct the same to said concave mirror.
 6. An imaging optical system according to claim 3, wherein said half waveplate is disposed between said polarization beam splitter and said third lens group.
 7. A projection exposure apparatus for projecting a pattern of mask onto a substrate, comprising:a polarization beam splitter; a quarter waveplate; a reflection mirror; and polarization plane changing means; wherein a beam from the mask is projected by way of said polarization beam splitter and said quarter waveplate upon said reflection mirror, wherein the projected beam is reflected by said reflection mirror and is projected by way of said quarter waveplate and said polarization beam splitter upon the substrate, and wherein said polarization plane changing means is disposed between said polarization beam splitter and the substrate to change the plane of polarization of the beam from said beam splitter, wherein said polarization plane changing means comprises a half waveplate effective to transform a beam from said polarization beam splitter into a rectilinearly polarized beam, being polarized in a desired direction.
 8. A projection exposure apparatus for projecting a pattern of mask onto a substrate, comprising:a polarization beam splitter; a quarter waveplate; a concave mirror; and a half waveplate; wherein a beam from the mask is projected by way of said polarization beam splitter and said quarter waveplate upon said concave mirror, wherein the projected beam is reflected by said concave mirror and is projected by way of said quarter waveplate and said polarization beam splitter upon the substrate, and wherein said half waveplate is disposed between said polarization beam splitter and the substrate to change the beam from said beam splitter to a linearly polarized beam, being polarized in a desired direction.
 9. An apparatus according to claim 8, further comprising a first lens group disposed between the mask and said polarization beam splitter and a third lens group disposed between said polarization beam splitter and the substrate.
 10. An apparatus according to claim 9, wherein said first lens group is effective to transform a beam from the mask into a parallel beam and to project the parallel beam to said polarization beam splitter.
 11. An apparatus according to claim 10, further comprising a second lens group disposed between said polarization beam splitter and said concave mirror, wherein said second lens group is effective to transform the parallel beam from said polarization beam splitter into a divergent beam and to direct the same to said concave mirror.
 12. An apparatus according to claim 9, wherein said half waveplate is disposed between said polarization beam splitter and said third lens group.
 13. A device manufacturing method for manufacturing micro devices using a projection exposure apparatus which projects a pattern of a mask onto a substrate, comprising a polarization beam splitter, a quarter waveplate, a concave mirror, and a half waveplate disposed between the polarization beam splitter and the substrate, wherein said method comprises the step of projecting a device pattern of the mask onto the substrate to transfer the device pattern of the mask to the substrate by:projecting a beam from the mask by way of the polarization beam splitter and the quarter waveplate upon the concave mirror; reflecting the projected beam from the concave mirror via the quarter waveplate and the polarization beam splitter toward the substrate; and changing the projected beam reflected from the concave mirror toward the substrate to a linearly polarized beam polarized in a desired direction by the half waveplate. 